It is difficult for a wheelchair occupant to ascend and descend curbs and the like when moving between the roadway and a sidewalk or the like. In certain cases, where the self-propelled wheelchair occupant possesses great strength in the arms and shoulders, it is possible to "hop" the wheelchair up a curb by leaning rearwardly in the wheelchair to position the small front wheels up onto the curb and then physically rotating the large drive wheels to engage and move up onto the curb elevated surface. However, this "hopping" maneuver of a conventional self-propelled wheelchair requires considerable skill and strength and it is not possible for many wheelchair occupants to maneuver curbs in this manner. In order to prevent tipping the wheelchair over in a rearward direction during this type of curb "hopping" maneuver, U.S. Pat. No. 3,848,883 proposes the addition of anti-tipping wheels positioned rearwardly of the large drive wheels.
It has long been recognized that there is a need for a self-propelled wheelchair for easily ascending and descending curbs and the like. For example, a climbing wheelchair is disclosed in U.S. Pat. No. 3,304,094 which is equipped with elliptical wheels associated with the main drive wheels and fluid pressure operated pistons associated with the front guide wheels for permitting the wheelchair to ascend and descend a curb or the like. However, the pistons are operated by compressed air bottles which must be frequently refilled and the elliptical wheels associated with the main drive wheels require a complicated drive arrangement which adds considerable complexity and cost to the wheelchair.
U.S. Pat. No. 3,573,877 discloses a lever operated main drive wheel lifting plunger for vertical movement downwardly beneath the main drive wheel. This lever operated plunger may be manually lowered to raise the main drive wheel upwardly to the level of the curb but the front guide wheels of the wheelchair must be positioned up on the curb before the main drive wheel is lifted by the lever operated plunger by tilting the wheelchair backward, and this requires more physical effort than is available to many wheelchair occupants.
U.S. Pat. No. 4,455,029 discloses a wheelchair with auxiliary front and rear wheels which are operated by a lever mechanism to lift the wheelchair as it is moved forwardly onto a curb. The lever operated auxiliary lifting wheels of this patent are also difficult to operate and require a complicated linkage between the operating handle and the auxiliary wheels.